There isn't much loss of quality provided the correction isn't too severe. I've just processed a load of shots taken at an exhibition yesterday, where I couldn't hold the camera level and get everything in (my excuse
) and the final IQ is OK even for those taken at ISO 1600. It's better to do the corrections on the original RAW (I use BIbble + Percy Pro plugin, which is neat) or a 16-bit TIFF. Doing it with a small JPEG is likely to lose something.